There are many counterarguments listed on the Open Borders site, and for that I give him credit. Especially as he actually attempts to engage with racialist arguments, rather than dismissing them.

I'm not sure if it's a technique worth crediting. There are voting trend issues with Hispanic immigrants that do not boil down to paranoid delusions about the Reconquista, and there are arguments regarding crime and immigration that are strongly and obviously distinguishable from sending every African-American person -- including those innocent of any crime -- out of the country. I'm hard-pressed to believe those arguments were selected for any reason but their weakness and unpalatability.

I personally favor reduced barriers to immigration (outside of a criminal background check and unique person identification, the modern limits are counterproductive at best), but writing up the worst arguments against that belief doesn't really strengthen them.